1. Field of the Invention
The present invention relates to a tripod constant velocity universal joint for use in a drivetrain of an automobile, for example, for transmission of torque with constant angular velocity between two rotary axes at any angle and allowing axial displacement.
2. Description of the Background Art
Generally, a tripod constant velocity universal joint comprises an outer joint member adapted to be connected to a first rotary shaft for transmission of torque and having three, circumferentially equispaced, axially extending track grooves formed in an inner circumference thereof, an inner joint member having a boss adapted to be connected to a second rotary shaft for transmission of torque and three circumferentially equispaced journals radially protruding from the boss, and rollers interposed between the outer joint member and the inner joint member to transmit torque.
In the tripod constant velocity universal joint, there is a high possibility that a journal bottom part is a weakest part of the inner joint member in strength. Japanese unexamined patent publication 2004-257418 discloses a tripod constant velocity universal joint of so-called double roller type in which an outer roller rolls in parallel to a track groove to realize reduction in weight and size while maintaining the strength of the inner joint member.
The tripod constant velocity universal joint described in Japanese unexamined patent publication 2004-257418 is characterized in that the journal bottom part of the inner joint member is of a non-circular cross section with a diameter measured circumferentially of the joint being larger than a diameter measured axially of the joint. Thus, reduction in size, weight and costs of the joint can be realized while maintaining the strength of the journal bottom part as a possible weakest part of a trunnion in strength.